Optically active oxazoline compounds, liquid crystal composition containing the same and optical switching method using the same

ABSTRACT

The present invention discloses novel optically active oxazoline compounds represented by the formula (I): ##STR1## wherein R 1  represents an alkoxy group having not more than 20 carbon atoms and R 2  represents a low grade alkyl group, as well as liquid crystal compositions containing said compound and a switching mode of high response speed using them. Furthermore, the invention discloses that the devices using said liquid crystal compositions can suitably be used in the opto-electronics field not only for display device but also as various electro-optic devices.

This is a division, of application Ser. No. 07/704,935, filed on May 23,1991, U.S. Pat. No. 5,159,084.

BACKGROUND OF THE INVENTION

The invention relates to novel optically active oxazoline compoundsrepresented by the formula (I): ##STR2## as well as liquid crystalcompositions containing them and an optical switching method using them.

So far, conventional liquid crystals have widely been used as materialsfor display devices. In most cases, these display devices are based onTwisted Nematic (hereinafter, referred to as "TN") mode using nematicliquid crystals, so that they have a disadvantage that almost all theresponse speeds of them are extremely low, namely, as slow as severalmilliseconds at the fastest.

In order to eliminate this disadvantage of TN mode, various attemptshave been made. For example, a display method using a ferroelectricliquid crystal is disclosed in N. A. Clarks et al., Applied phys. Lett.36, 899 (1980). This method uses chiral smectic phase, particularlychiral smectic C phase, liquid crystal and attracts attention as amaterial for a high speed optical switching. Some ferroelectric liquidcrystal materials using this principle have already been known [forexample, refer to Japanese Patent Application Laid Open No. 70,455[1989]. However, no material having satisfactory properties has beenknown yet.

The present inventors have studied intensively in order to develope aliquid crystal having satisfactory properties to be used for an opticalswitching method. Finally, they have found that the oxazoline compoundsrepresented by the formula (I) satisfies the requirements. The inventionhas been completed based on this finding.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an infrared absorption spectrum of an oxazoline compoundprepared in Example 1 of the present invention.

SUMMARY OF THE INVENTION

An object of the present invention is to provide novel oxazolinecompounds represented by the formula (I): ##STR3##

Another object of the present invention is to provide liquid crystalcompositions containing a oxazoline compounds represented by the formula(I).

Still another object of the present invention is to provide a liquidcrystal material which has high response speed, is chemically stable andsuits for an optical switching method.

Yet another object of the present invention is to provide an opticalswitching method using said optically active oxazoline compounds or aliquid crystal composition thereof.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to novel oxazoline compounds representedby the formula (I): ##STR4## wherein R¹ represents an alkoxy grouphaving not more than 20 carbon atoms, R² is a low grade alkyl groupand * indicates a asymmetric carbon atom; as well as a liquid crystalcomposition containing said compound and an optical switching methodusing said compound or said composition.

The term, "liquid crystal composition" in the present invention means acomposition comprising a liquid crystal and another liquid crystaland/or a compound other than a liquid crystal such as a chiral compoundand still having a liquid crystal phase. As a "low grade alkyl group",an alkyl group having 1 to 8 carbon atoms is preferable, the grouphaving 1 to 4 carbon atoms is more preferable, and the group having 1 to2 carbon atoms is further preferable.

The largest characteristic of the oxazoline compounds represented by theformula (I) of the present invention is that they have an asymmetriccarbon atom is their oxazoline ring. Since the compounds have anasymmetric carbon atom at α-position of a group having a dipole momentin a direction perpendicular to a molecular axis, their electricproperties, such as spontaneous polarization in a liquid crystal phaseare improved remarkably.

Namely, the optically active oxazoline compounds represented by theformula (I) of the present invention show excellent properties as aferroelectric liquid crystal. They have high response speed and arechemically stable. As for an optical switching method using theoxazoline compound of the present invention, a switching method having aresponse speed of not more than 1 m second is preferably used. Moreover,by adding said compound to a nematic liquid crystal, the occurrence ofreverse domain in a TN type cell can effectively be prevented.

Therefore, the liquid crystal compositions containing the oxazolinecompound represented by the formula (I) of the present invention cansuitably be used not only for display device, but also as variouselectro-optic devices such as an electro-optic shutter, an electro-opticiris diaphragm, an optical modulator, a switch for changing optical pathfor optical communication, a memory and a lens with variable focallength.

Practical examples of the optically active oxazoline compoundsrepresented by formula (I) are shown in Table 1.

                  TABLE 1                                                         ______________________________________                                        Compound                                                                      No.             R.sup.1       R.sup.2                                         ______________________________________                                        1               C.sub.16 H.sub.33 O--                                                                       C.sub.2 H.sub.5 --                              2               C.sub.14 H.sub.29 O--                                                                       C.sub.2 H.sub.5 --                              3               C.sub.12 H.sub.25 O--                                                                       C.sub.2 H.sub.5 --                              4               C.sub.10 H.sub.21 O--                                                                       C.sub.2 H.sub.5 --                              5               C.sub.9 H.sub.19 O--                                                                        C.sub.2 H.sub.5 --                              6               C.sub.8 H.sub.17 O--                                                                        C.sub.2 H.sub.5 --                              7               C.sub.7 H.sub.15 O--                                                                        C.sub.2 H.sub.5 --                              8               C.sub.6 H.sub.13 O--                                                                        C.sub.2 H.sub.5 --                              9               C.sub.5 H.sub.11 O--                                                                        C.sub.2 H.sub.5 --                              10              C.sub.16 H.sub.33 O--                                                                       CH.sub.3 --                                     11              C.sub.14 H.sub.29 O--                                                                       CH.sub.3 --                                     12              C.sub.12 H.sub.25 O--                                                                       CH.sub.3 --                                     13              C.sub.10 H.sub.21 O--                                                                       CH.sub.3 --                                     14              C.sub.9 H.sub.19 O--                                                                        CH.sub.3 --                                     15              C.sub.8 H.sub.17 O--                                                                        CH.sub.3 --                                     16              C.sub.7 H.sub.15 O--                                                                        CH.sub.3 --                                     17              C.sub.6 H.sub.13 O--                                                                        CH.sub.3 --                                     18              C.sub.5 H.sub.11 O--                                                                        CH.sub.3 --                                     ______________________________________                                    

These compounds of the formula (I) can generally be obtained by reactinga nitrile compound of the formula (II) with an optically active2-amino-alcohol compound of the formula (III) in the presence of acatalyst.

As a catalyst to be used for the reaction, cadmium acetate, cadmiumchloride, zinc chloride and cobalt chloride can be exemplified. Thecatalyst is added preferably in an amount of 10⁻⁵ to 10⁻¹ mol per 1 molof the nitrile compound.

The reaction can usually be carried out without any solvent or in aninert solvent such as an aromatic hydrocarbon. The reaction is carriedout at a temperature of 80° to 200° C., preferably 100 to 150° C.##STR5## wherein, R¹ represents an alkoxy group having not more than 20carbon atoms. ##STR6## wherein, R² is a low grade alkyl group, and *indicates an asymmetric carbon atom.

The optically active oxazoline compounds represented by the formula (I)of the present invention show excellent properties as a ferroelectricliquid crystal material. They have high response speed and arechemically stable.

The novel optically active oxazoline compound represented by the formula(I) of the present invention can be used by itself as a ferroelectricliquid crystal material, but, it can also be mixed with a smectic liquidcrystal which in itself is not chiral, or with another ferroelectricliquid crystal material, to obtain a liquid crystal composition havingan improved performance.

Furthermore, by adding the optically active oxazoline compoundrepresented by the formula (I) to a nematic liquid crystal, theoccurrence of reverse domain can effectively be prevented. In this case,said oxazoline compound is used preferably at an amount of 0.01 to 50%by weight of the liquid crystal composition to be obtained.

Moreover, by adding said oxazoline compound to a nematic liquid crystalor to a chiral nematic liquid crystal, it can be used as a chiralnematic liquid crystal composition for a phase transition type liquidcrystal device or a guest-host type liquid crystal device. In this case,said oxazoline compound is used preferably at an amount of 0.01 to 80%by weight of the liquid crystal composition to be obtained.

The liquid crystal composition containing the compound of the presentinvention can suitably be used in the electro-optic devices such as anelectro-optic shutter, an electro-optic iris diaphragm, an opticalmodulator, a switch for changing optical path for optical communication,a memory and a lens with variable focal length.

The compound of the present invention can be used in combination withvarious liquid crystal compounds, but, it is preferably used incombination with those showing ferroelectric chiral smectic phase, andmore preferably in combination with those listed in Table 2.

    TABLE 2      No. Chemical Structure and Name of Compound Phase Transition Temperature      (°C.)          1      ##STR7##      ##STR8##      2     ##STR9##      ##STR10##      3     ##STR11##      ##STR12##      4     ##STR13##      ##STR14##      5     ##STR15##      ##STR16##      6     ##STR17##      ##STR18##      7     ##STR19##      ##STR20##      8     ##STR21##      ##STR22##      9     ##STR23##      ##STR24##       10      ##STR25##      ##STR26##       11      ##STR27##      ##STR28##       12      ##STR29##      ##STR30##       13      ##STR31##      ##STR32##       14      ##STR33##      ##STR34##       15      ##STR35##      ##STR36##     Foot Note:     SmC*; Ferroelectric smectic C phase  Iso; Isotropic phase     SmA; Smectic A phase  Cr; Crystalline phase     SmH*; Ferroelectric smectic H phase  Cho; Choleteric phase     Sm3; Smectic phase

EXAMPLES

The invention will be explained more in detail with reference to thefollowing examples, but, the invention is not limited thereto. As tophase transition temperatures in the examples, the values thereof varyslightly depending on a measurement method and a purity of thecompounds.

EXAMPLE 1 Preparation of optically active2-[4'-(4"-n-dodecyloxyphenyl)phenyl]-5-ethyl-2-oxyazoline [Compound No.3 in Table 1]

3.65 g (0.01 mol) of 4-n-dodecyloxy-4'-cyanobiphenyl, 1.14 g (0.015 mol)of (R)-2-amino-1-butanol and 0.27 g of cadmium acetate dihydrate wereheated and refluxed for 30 hours in toluene. After cooling to roomtemperature, an inorganic substance was removed by filtration. A residueobtained by distilling out the toluene was treated with a silica gelcolumn chromatography using 1,2-dichloroethane as a developing solvent.The thus obtained crude objected substance was recrystallized threetimes in ethanol to obtain 2.32 g of pure objected substance [CompoundNo. 3].

As an angle of rotation of compound [α]^(D) =+24.50 (in chloroform) wasobserved. The structure of this compound was confirmed by an infraredabsorption spectrum, which is shown in FIG. 1.

EXAMPLES 2 to 6

Compounds 4 to 8 in Table 1 were synthesized by the same method as inEXAMPLE 1 except that R¹ in the compound of formula (II) was changedaccordingly. The chemical structure (only R¹ is indicated), elementalanalysis value and the phase transition temperature of each of thecompounds are listed in Table 3 together with those of Compound 3 ofEXAMPLE 1.

                                      TABLE 3                                     __________________________________________________________________________     ##STR37##                                                                                       Elementary Analysis                                            Compound       Measured Value                                                                         Calculated Value                                                                       Phase Transition                         Ex. No.    R.sup.1 (%)      (%)      Temperature (°C.)                 __________________________________________________________________________    1   (3)    n-C.sub.12 H.sub.25 O                                                                  C H N                                                                           79.98  9.51  3.20                                                                    C H N                                                                           79.95  9.49  3.22                                                                    ##STR38##                               2   (4)    n-C.sub.10 H.sub.21 O                                                                  C H N                                                                           79.44  9.25  3.45                                                                    C H N                                                                           79.56  9.15  3.44                                                                    ##STR39##                               3   (5)    n-C.sub.9 H.sub.19 O                                                                   C H N                                                                           79.29  9.01  3.61                                                                    C H N                                                                           79.35  8.96  3.56                                                                    ##STR40##                               4   (6)    n-C.sub.8 H.sub.17 O                                                                   C H N                                                                           79.12  8.76  3.69                                                                    C H N                                                                           78.98  8.96  3.90                                                                    ##STR41##                               5   (7)    n-C.sub.7 H.sub.15 O                                                                   C H N                                                                           78.64  8.66  3.45                                                                    C H N                                                                           78.86  8.55  3.44                                                                    ##STR42##                               6   (8)    n-C.sub.6 H.sub.13 O                                                                   C H N                                                                           78.64  8.27  3.97                                                                    C H N                                                                           78.60  8.32  3.99                                                                    ##STR43##                               __________________________________________________________________________

[In the above Table 3, Cryst. means crystalline state, Iso meansisotropic liquid, Sc* means chiral smectic C phase and Sx means asmectic phase but can not clearly identified.]

EXAMPLE 7 Preparation of optically active2-[4'-(4"-n-decyloxyphenyl)phenyl]-6-methyl-2-oxazoline [Compound No. 13in Table 1]

3.35 g (0.01 mol) of 4-n-decyloxy-4'-cyanobiphenyl, 1.13 g (0.015 mol)of (S)-2-aminopropanol and 0.27 g of cadmium acetate dihydrate wereheated and refluxed in toluene for 30 hours. After cooling to roomtemperature, an inorganic substance was removed by filtration. A residueobtained by distilling out the toluene was treated with a silica gelcolumn chromatography using 1,2-dichloroethane as a developing solventto obtain a crude objected substance. The crude substance wasrecrystallized three times in ethanol to obtain 1.42 g of pure objectedsubstance [Compound No. 13].

The structure of this compound was confirmed by an infrared absorptionspectrum.

EXAMPLES 8 to 10

Compounds 14 to 16 in Table 1 were synthesized by the same method as inEXAMPLE 7 except that R¹ in the nitrile compound of the formula (II) waschanged accordingly. The chemical structure (only R¹ is indicated),elemental analysis value and the phase transition temperature of each ofthe compounds are listed in Table 4 together with those of Compound No.13 of EXAMPLE 7.

                                      TABLE 4                                     __________________________________________________________________________     ##STR44##                                                                       Compound     Elementary Analysis   Phase transition Temperature            Ex.                                                                              No.   R.sup.1                                                                              Measured Value (%)                                                                       Calculated Value (%)                                                                     (°C.)                            __________________________________________________________________________    7  (13)  n-C.sub.10 H.sub.21 O                                                                  C H N                                                                           79.22  9.04  3.53                                                                      C H N                                                                           79.35  8.96  3.56                                                                     ##STR45##                              8  (14)  n-C.sub.9 H.sub.19 O                                                                   C H N                                                                           78.98  8.94  3.65                                                                      C H N                                                                           79.12  8.76  3.69                                                                     ##STR46##                              9  (15)  n-C.sub.8 H.sub.17 O                                                                   C H N                                                                           78.84  8.80  3.84                                                                      C H N                                                                           78.87  8.55  3.83                                                                     ##STR47##                              10 (16)  n-C.sub.7 H.sub.15 O                                                                   C H N                                                                           78.40  8.50  3.92                                                                      C H N                                                                           78.60  8.32  3.99                                                                     ##STR48##                              __________________________________________________________________________

[In the above Table 4, Cryst. means crystalline state, Iso. meansisotropic liquid and Sc* means chiral smectic C phase.]

APPLICATION EXAMPLES APPLICATION EXAMPLE 1

Two transparent electrodes were coated on their surface with polyvinylalcohol (PVA). The surfaces was then subjected to a parallel orientationtreatments by means of rubbing. The electrodes were set facing eachother with a distance of 3 μm formed a cell making the PVA films innersides and the optically active oxazoline compound of EXAMPLE 4 [compoundNo. 6] was injected into the cell. The cell obtained was placed betweentwo polarizers which were placed perpendicular to each other andobtained a liquid crystal display device. When a voltage of 30 V wasapplied between the electrodes, a switching action of a high responsespeed (ca. 100μ second) was observed.

The spontaneous polarization of this liquid crystal was 28.5 nc/cm² at100° C.

APPLICATION EXAMPLE 2

A composition of the compound No. 3 prepared in Example 1 was preparedby mixing 21% by weight of p-octyloxy-benzoicacid-p'-n-hexyloxyphenylester. This composition had the following phasetransition points: ##STR49## Wherein

Cryst: Crystalline state,

SmC*: Ferroelectric smectic C phase,

Ch: Cholesteric phase

Iso: Isotropic liquid.

What is claimewd is:
 1. A display device and an electro-optic deviceprovided with a liquid crystal composition with an optical switchcomprising an optically active oxazoline compound represented by theformula (I): ##STR50## wherein R¹ is an alkoxy group having not morethan 20 carbon atoms and R² is an alkyl group having 1 to 8 carbonatoms.
 2. A display device and an electro-optic device provided with anoptical switch comprising an optically active oxazoline compound of theformula (I) as a liquid crystal: ##STR51## wherein R¹ and R² have thesame meaning as those in claim
 1. 3. The display device and theelectro-optic device according to claim 1, wherein said compositionfurther contains a nematic liquid crystal.
 4. The display device and theelectro-optic device according to claim 1, wherein said compositionfurther contains a chiral nematic liquid crystal.
 5. The electro-opticdevice according to claims 2 or 3, wherein said device is selected fromthe group consisting of an electro-optic shutter, an electro-optic irisdiaphragm, an optical modulator, a switch for changing optical path foroptical communication, a memory and a lens having variable focal length.